I've run groups of 6-8 people fairly regularly - usually with Savage Worlds (or recently C&C) so the combat system is by nature a bit quicker, but I think some of these should still apply. Here are some suggestions, in no particular order:
Splitting up is bad. Whille tempting, I've found it makes it that much harder to focus screen time on each character, since now you've got two narratives to deal with, not one. Keep 'em together whenever possible.
Have players roll whenever possible. Have them roll to hit, damage and saves for the monsters and NPCs. It works really well in combat to have each player roll for their opponents. They might metagame a little ("Oh, so the BBEG is AC 25"), but really, so what? Have them roll every save of their own possible. I reserve the right to roll Search checks, but have them roll - and then roleplay - just about everything else.
Insist on readable dice. I have a player who likes to bring whatever new dice he bought, and 90% of the time they are totally unreadable from more than a foot away. Those aren't allowed anymore. At least the guy next to you has to be able to read the damn things.
Pay attention to space. Sometimes a good tactical challenge for a large group is simply a smaller corridor or some kind of bottleneck. (We had a great scene where the group was fighting an Otyugh, who was at the top of a staircase that was only 10' wide, so only so many characters could fight it at once. One made a heroic effort to slide under the Otyugh to get around it. Great fun.)
Mooks are your friend. With a large group, you don't really need more BBEGs, you just need more mooks (which makes it that much more valuable to have players make attack/damage rolls for their opponents). I like using a gang-up rule (stolen from Savage Worlds, +1 to hit for each adjacent ally engaged with the same enemy) for big parties - its both good for and against, but it helps increase the potency of mooks.
Use shortcuts whenever possible. For example, many of my mooks get rated in brackets; 2 HP, 8 HP, etc - or in DM shorthand, one-hitters, two-hitters, etc. So instead of bookkeeping HP, I keep tracks of hits (crits counting as two or even three), and the mooks go down in that number of hits.
Document important SOPs. What are the marching orders, outside, inside, 5' corridor, 10' corridor? Who usually carries what kind of weapons out? Who has the light sources? Etc. Once its documented, assume its that way unless specifically told otherwise.
Five second rule. When its your turn in combat, you have 5 seconds to tell me what you want to do. Don't hem or haw, or your character is automatically holding. Heck, when its your turn out of combat, same thing. Questions are fine, but indecision is not.
Treat out of combat a lot like combat. Out of combat can be a huge time drain if everyone is talking at once. I tend to treat it a bit like combat, and go around the table and ask each person what they're doing. I usually try to rotate one direction around the table and then back around the other, so that the same people aren't always first to speak. My general rule is that if more than two people want to talk at the same time, then I should probably go around the table.
Control the narrative. This is really a corollary to the above, but it merits saying again. Eight players at the table become random and unorganized (and more importantly, unfun) very quickly - your job is to keep that from happening. Have a non-verbal cue for when you want to talk without interruption/questions (such as when you're reading a description or something similar), be decisive when asked questions, assigning difficulties and making rulings, and make sure not to favor the loudest or more talkative (this last point is always important, but more important and more difficult with a bigger group).
Figure out when NOT to control the flow. For all of the notes listed above about being quick, and going around the table and controlling the narrative, there are a few good times to ditch that 100%. A good example is when multiple characters get into a discussion about something in the game (tactics, treasure, puzzles, etc). Let the in-character conversations rip. (I'm less generous about player conversations.)
Breathe every now and then. Its easy to get completely caught up running a game with that many folks. Or at least, is it for me. I make sure to take a few deep breathes every now. DMing is supposed to be fun.
I love DMing large groups - I really enjoy the dynamic of that many people working together for a common goal (to have fun).
